Offshore hydrocarbon production platforms are commonly fixed to the soil floor of a body of water by foundation piles and well conductors that extend from the floor to the platform. The piles and conductors are fabricated from open-ended steel pipes. The pipe is installed by driving an open end of the pipe into the soil floor down to a predetermined design penetration depth that is sufficient to firmly anchor the pipe in the floor. Installation typically employs an impact hammer to drive the pipe into the soil, applying repeated impacts with the hammer to the top of the pipe. The force of the impact must be sufficient to overcome the resistance of the soil to penetration by the pipe.
Installation problems often occur in dense unconsolidated cohesionless soils, such as sands or silts. The resistance of these types of soils to penetration by the pipe is extremely difficult to predict. Consequently, advance design of pipe installations in such soils has an inherently high degree of uncertainty. In many cases the pipe installer unexpectedly experiences "refusal" prior to reaching the predetermined design penetration depth in the soil when the number of impacts required to advance the pipe a given distance in the soil becomes impractically high. Refusal is generally attributable to the plug of soil that forms in the interior of the pipe as the open end advances through the soil. The plug has a relatively high resistance to penetration by the pipe. An accepted remediation technique upon experiencing refusal is to physically remove the soil plug from the pipe interior. Removal is accomplished by drilling the plug out from the pipe interior or jetting the plug out with high pressure steam or water. However, these are relatively costly and time consuming procedures that are advantageously avoided where possible. It is apparent that a need exists for alternate means of installing a pipe in a subsurface soil.
Accordingly, it is an object of the present invention to provide an effective method for installing a pipe in a subsurface soil by reducing the resistance of the soil to installation of the pipe therein. More particularly, it is an object of the present invention to provide a method for installing a foundation pile or well conductor associated with an offshore hydrocarbon production facility in a soil floor. It is another object of the present invention to provide such an installation method that does not require substantial modification to the conventional design of the piles or conductors being installed. It is still another object of the present invention to provide such an installation method that can be performed with conventional construction equipment. It is yet another object of the present invention to provide such an installation method that does not result in a diminished load-bearing capacity of the installed piles or conductors. It is a further object of the present invention to provide such an installation method that avoids the step of removing the plug from the interior of the pile or conductor. These objects and others are achieved in accordance with the invention described hereafter.